1. Field of the Invention
The present invention relates to an image-capturing technique. More particularly, the present invention relates to a technique for processing image abnormality caused by power supply.
2. Description of Related Art
With development of digital still camera (DSC) techniques, and progress of digital signal processing techniques, besides a high resolution, a high-ISO performance of the DSC is also pursued in the market. However, technique problems are also generated. To achieve the high resolution, more sensing pixels are required, so that a larger current is required to transmit data (image). In case that the high-ISO is required and the sensing pixels are not increased, an analogue gain has to be increased. Under such a strict condition, a speed of a transient response of a power system can also influence an image quality.
FIG. 1 is a block diagram illustrating a commonly used DSC system. Referring to FIG. 1, the DSC 90 includes a digital signal processor (DSP) 100, an analogue front end (AFE) unit 96, a charge coupled device (CCD) 98, a low drop-out (LDO) voltage regulator 94, and a power supply 92, wherein the LDO voltage regulator 94 can also be a DC/DC converter. A function of the LDO voltage regulator 94 or the DC/DC converter 94 is used for supplying power to the circuit units. The DSP 100 controls operations of the whole system (including operations of the AFE processing unit 96 and the CCD 98). When the AFE processing unit 96 receives a horizontal sync signal Hsync from the DSP 100, the AFE processing unit 96 outputs a horizontal and a vertical control signals ΦH and ΦV to the CCD 98, and simultaneously receives an output signal OS from the CCD 98. The image data of the output signal OS is processed by an ADC/AGC 116 and an ADC 110, and is converted from an analogue signal to a digital signal, and then is transmitted to the DSP 100. This is an image processing process of the DSC 90. The DSP 100 can also control a lens driver 124 to interactively control a lens module 126.
Other elements such as memory devices RAM 104 and ROM 106, and a LCD panel 102 are used for displaying images. Further, the AFE processing unit 96 further includes a timing generator (TG) 108, and the TG 108 respectively generates a horizontal clock and a vertical clock to a horizontal driver 112 and a vertical driver 114. The LDO voltage regulator 94 provides a horizontal voltage VΦH and a horizontal current IΦH to the horizontal driver 112 for driving the image on horizontal scan lines. The image sensed by the CCD 98 is output by line data one after another.
Since at an initial stage, the horizontal current IΦH has an inrush noise of transient oscillation, a quality of the front part of the output image is influenced. For example, vertical stripes, horizontal stripes, ghosts, pits, etc., may all severely influence the quality of the image.
FIG. 2 is a timing diagram of a conventional image transmission. FIG. 3 is an amplified diagram of an initial section 140 during the conventional image transmission of FIG. 2. Referring to FIG. 2, FIG. 2 is a timing diagram of the horizontal sync signal Hsync, the horizontal control signal ΦH, the horizontal voltage VΦH and the horizontal current IΦH, etc. The horizontal control signal ΦH is a horizontal shift clock. When the AFE processing unit 96 outputs the horizontal control signal ΦH to the CCD 98, a transient high current about 100 mA can be generated. The horizontal driver 112 used for outputting the horizontal control signal ΦH may have an unstable current and voltage due to such transient high current, so that the analogue signal of the image of the CCD 98 at the initial section of a left part can be interfered to having noises such as vertical stripes, etc. Such unstable current and voltage phenomenon is shown as the initial section 140, and an amplified diagram thereof is shown as FIG. 3.
Referring to FIG. 3, by amplifying the initial section 140 that the horizontal control signal ΦH is initially transmitted, it is obvious that when the current is unstable, the initial section 140 exceeds a dummy pixel region 142 of a line data of a horizontal image, and some of pixel regions 146 belonged to the effective pixel region 144 has been transmitted. Namely, since the current is unstable at the initial section, bad pixels at the pixel region 146 can influence the image quality of a left part (an initial position) of the CCD image that corresponds to the region 146, which is a main reason that causes the noise.
Therefore, at least the aforementioned problem of image noise has to be resolved.